Small-area electroluminescent diodes that can be current-modulated at relatively high current densities and at room temperatures are finding increasing uses as transmitting sources for multimode optical fiber communication lines. Thanks to modern liquid phase epitaxy (LPE) deposition techniques and other techniques now highly developed for manufacture of integrated circuits and diffused-junction planar semiconductor devices, such light-emitting diode structures can now be made small enough for relatively efficient coupling to the end of an optical communication fiber whose active light-transmitting area may have a very small diameter ranging from a few microns up to 100 microns or so.
Numerous forms of light-emitting diodes (LED's) have been developed for such purposes and are described in the published art. For example, one available type of surface-emitting LED incorporates a double heterojunction structure as described in an article appearing in "Optical Fiber Technology" on pages 306-308, copyright 1976 by IEEE Press, and in turn stated to be reprinted with permission from "Optics Communications", Vol. 4, December 1971, pages 307-309. This article, by C. A. Burrus and B. I. Miller of Bell Telephone Laboratories, describes briefly what has been sometimes called in the trade a "Burrus diode". It is with this general class of LED's that our invention is concerned.